It is often necessary to couple together shafts which are not precisely in alignment with each other or which are mounted in respective mechanisms that have some freedom of movement relative to each other, such that a rigid coupling of the shafts is impossible. Various forms of flexible couplings are known for use in these situations that are able to allow for both angular and parallel misalignment of the shafts.
One well-known arrangement is the coupling in which an intermediate shaft has universal joints of the Hooke or Cardan type at opposite ends connecting it to the respective shafts. Such a construction has a number of disadvantages, in particular as regards the minimum axial space required to accommodate the coupling and to permit its assembly and removal if the shafts to be coupled are already in place. It is also relatively complex and therefore expensive to produce, and its usefulness is generally confined to arrangements in which it is necessary to accommodate large misalignments.
It has also been proposed to provide a flexible coupling using an intermediate member that is itself of a flexible nature, in particular a group of leaf springs (U.S. Pat. No. 1,712,219) or a rubber tube (U.S. Pat. No. 2,908,150). Such constructions have the merit of simplicity but they must have a relatively large axial length to accommodate any significant misalignment. They are therefore cumbersome and are limited in the torque they can transmit and, moreover, because of the flexible nature of the intermediate member they can be unstable at high speeds of rotation.